1. Field of the Invention
The present invention relates to a passenger (state) detection apparatus for detecting a seated state of a passenger seated in a vehicle, in particular, a passenger detection apparatus which can detect a breakage on a shield line for connecting a detector main body (i.e., control box) and a sensor.
Priority is claimed on Japanese Patent Application No. 2006-265539, filed Sep. 28, 2006, the content of which is incorporated herein by reference.
2. Description of the Related Art
In recent vehicles such as an automobile for riding, it is required to detect seated states, such as whether an adult or a child is sitting on a passenger seat (or an assistant driver's seat), or whether a child seat is installed on a passenger seat. This is because when an airbag apparatus is installed at a passenger seat, control for making an airbag operable or inoperable should be performed depending on the seated state of the passenger seat.
Conventionally, a passenger detection apparatus for detecting such a seated state has been developed (see Patent Document 1). In the disclosed passenger detection apparatus, a sensor for detection is attached to a target seat in a vehicle, and a high-frequency low voltage is applied to this sensor. The seated state of a passenger is determined by using a phenomenon such that the current, which flows through the sensor, changes depending on the state of the passenger on the target seat.    Patent Document 1: Japanese Patent No. 3353817
In the above conventional passenger detection apparatus, a high-frequency low voltage is used, and thus a shield line is employed for connecting the control box to the sensor. If breaking of the shield line occurs, passenger (state) detection may not be accurately performed. Therefore, a technique for detecting a breakage of the shield line is required. However, in a state in which a plurality of shield cables are crowdedly bundled, detection of a breakage in the shield line may not be accurately performed. This is because when a plurality of shield cables are positioned close to each other, a stray capacitance between a shield line having a breakage and another shield line adjacent thereto appears, and a voltage of the adjacent shield line appears via the stray capacitance on the shield line having the breakage, so that it looks as if an accurate shield voltage were applied to the shield line having the breakage.